Recovering oil by cyclic steam injection combined with hot water drive



Jan. 14, 1969 D. s. KOONS 3,421,583

RECOVERING OIL BY CYCLIC STEAM INJECTION COMBINED WITH HOT WATER DRIVEFil'ed Aug. 30, 196'? PRODUCTION PRODUCTION CONTROLLER INVENTOR DAV! S.KOONS ATTORNEY SUPPLY STEAM GENERATOR WATER United States Patent Ofice3,421,583 Patented Jan. 14, 1969 7 Claims ABSTRACT OF THE DISCLOSUREThis specification discloses:

A method for producing oil from upper and lower oilbean'ng permeablestrata of a subterranean reservoir. Low-grade steam is separated intohot water and steam phases. The water and steam phases are introducedinto the lower and upper strata, respectively, from a first well for afirst period. For a second period, hot fluids which include oil areproduced from the upper strata through the first well. Cold water isindirectly heat exchanged with these hot fluids in the first well, andthen, the heated water is injected during the second period into thelower strata. As a result, a continuous hot water drive moves from thefirst well toward a second well in the lower strata during the first andsecond periods. Oil is produced from the lower strata through the secondwell. The water indirectly heated by the hot fluids in the first wellmay be about equal in volume to them, or any volume such that all of theinjected water is heated to above the initial temperature of thesubterranean reservoir.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a method of recovering oil from a subterranean reservoir.More particularly, it relates to a method employing steam and hot waterto produce oil from upper and lower strata in such reservoir.

Description of the prior art The injection of steam and production ofoil in alternate periods, through a single well, have been used toadvantage in recovering oil from a subterranean reservoir. One exampleof such procedure is described in U.S. Patent No. 3,292,702. In thisprocedure, steam is injected into the reservoir for a first period.Then, heated fluids in a liquid phase are produced from the reservoirfor a second period. Only one well is used in carrying out thisprocedure. The steam generating equipment commonly employed in such aprocedure produces steam of less than 100 percent in quality. Thislow-grade steam contains a significant hot water phase when injectedinto the reservoir. Commonly, the low-grade steam is of 80 percentquality, which means it contains, as a liquid phase, 20 percent of thewater from which the steam was formed.

The injected steam releases large amounts of heat upon its condensationto the liquid phase in the reservoir. As a result of the released heat,the recovery of oil from the reservoir is greatly improved when thesingle well is changed from an injection to a production function.

However, the hot water injected in a liquid phase with the steamreleases only a small part of its latent heat to the reservoir. Also,this hot water must first be pushed back into the reservoir by injectedsteam. Later, this water must be pushed by hot produced fluids from thereservoir back into the well during the production cycle. Thus, thewater is responsible for heating only a small part of the oil recoveredfrom the reservoir. However, this water wastes the energy of the steamand the hot produced fluids that move it between the reservoir and thewell. The wasted energy thereby reduces the amount of oil recovered froma given amount of injected steam. Also, the ever-present problems inpumping and separating oil from the produced fluids are furthermagnified by the large concentration of hot water and steam in theproduced fluids.

Summary of the invention In accordance with this invention, a method isprovided for producing oil from a subterranean reservoir having upperand lower oil-bearing permeable strata. These strata are penetrated byspaced first and second wells. An aqueous fluid is heated to atemperature suflicient to produce a low-grade steam. The steam containsa hot water phase at the pressure these fluids are injected into thestrata. The hot water phase is separated from the steam phase. The steamand hot water phases are injected into the upper and lower strata,respectively, via the first well, for a first period. Hot fluids areproduced from the upper strata through the first well for a secondperiod. Similutaneously, Water having a temperature less than theproduced hot fluids is passed through a separate flow path in indirectheat exchange with the hot fluids in the second period. The indirectlyheated water is injected in the second period into the lower strata, viathe first well, to effect a continuous hot water drive from the firstwell toward the second well in the lower strata, during the first andsecond periods. Oil is produced from the lower strata through the secondwell. Also, oil is included in the hot fluids produced from the upperstrata, via the first well, in the second period.

Description of the drawing The drawing illustrates, in vertical section,a subterranean reservoir having upper and lower oil-bearing permeablestrata, and various apparatus, by which the method of this invention canbe practiced.

Description of specific embodiments The drawing shows a subterraneanreservoir 10 which is comprised of upper and lower oil-bearing permeablestrata 11 and 12, respectively. The term oil as used herein includes allhydrocarbonaceous fluids recoverable from subterranean reservoirs. Anoverburden 13 resides above the strata 11. The strata 12 rest upon abedrock 14. The strata 11 and 12 are sufficiently isolated as to fluidflows so that separate oil-recovery procedures may be carried out,without interference, in them. The strata 11 and 12 may be the upper andlower portions of a thick geological structure containing recoverableoil. The strata 11 and 12 may be separated by an intervening shale, orother barrier structure, to restrict vertical fluid flows. Whatever thegeological status, the reservior 10 has a structure that steam may beinjected into the strata 11, and a hot water drive may be carried out inthe strata 12, without deleterious interaction between them. Moreparticularly, the hot water drive in the strata 12 should not moveupwardly to commingle with the fluids produced from the strata 11.

The reservoir 10 is provided with suitable means for the introductionand removal of the various fluids employed in the present method. Forexample, spaced first and second wells 16 and 17, respectively, extendfrom the earths surface 18 downwardly into the strata 11 and 12. Thewell 16 contains a casing 19 which extends through the strata 11 and 12to terminate adjacent bedrock 14. Openings 21 and 22 provide for fluidcommunication to the strata 11 and 12, respectively, from the interiorof the casing 19. A packer 23 in the casing 19 separates the well 16into two separate fluid zones. A conduit 24 extends downwardly in thewell 16 through the packer 23 and terminates adjacent the openings 22.

Similarly, a conduit 26 extends downwardly into the up per portion ofthe well 16 and terminates above the packer 23. A control valve 25 inthe conduit 26 regulates the flow of fluids therethrough. The fluids maybe pumped from the conduit 26, if desired. One or more openings 27 inthe conduit 26 provide for fluid flows to the upper portion of the well16 above the packer 23. A connecting conduit 28 traverses the packer 23and connects with the conduit 26 through a valve 29. The valve 29operates to regulate the flow of fluid in the conduit 28 through thepacker 23. The valve 25 is operatively interconnected to the valve 29. Adash line 31 indicates an operative interconnection for the selectiveoperation of the valves 25 and 29 at the earths surface 18. The valvesassociated with the well 16 may be operated manually, if desired.

Inlet conduits 32 and 33, respectively, connect a source of water, suchas water supply 34, and a source of lowgrade steam, such as steamgenerator 36, to the conduit 24. The inlet conduit 32 contains a valve37. The inlet conduit 33 contains a valve 38. The valves 37 and 38 maybe of any suitable design for regulating the flow of fluids through theconduits 32 and 33, respectively, into the conduit 24. The valves 37 and38 may be interconnected, as by dash line 31, in their operation to thevalves 25 and 29. A controller 39 may be used to regulate the variousfluid flows by adjusting the valves through an operative interconnectionillustrated by the dash line 31 in response to temperatures of thefluids in the well 16.

The well 17 has a casing 40 which extends downwardly into the strata 11and 12 and terminates adjacent the bedrock 14. One or more openings 41and 42 provide for the flow of fluids between these strata and the well17. A packer 43 separates the Well 17 into two fluid Zones. A conduit 44extends downwardly through the well 17 to below the packer 43. A conduit46 extends downwardly in the well 17 to above the packer 43. The well 17may be completed with a single tubing string and no packer where fluidproduction from strata 11 and 12 is commingled. The fluids may be pumpedfrom the well 17, if desired.

The fluids from the reservoir which flow through the conduits 26, 44,and 46 may be passed to a suitable production facility for theseparation of oil from other produced fluids. Production facilities arewell known, and any one of suitable construction to the functioning ofthe present invention can be used.

Although the reservoir 10, and various associated apparatus therewith,have been described in specific embodiments, other structures can beemployed to practice the present method.

In carrying out the method of the present invention, an aqueous liquid,from any source, is heated in the steam generator 36 to a temperaturesuflicient to produce a low-grade steam. The steam contains a hot waterphase at the pressure at which these fluids are injected into the strata11 and 12. Usually, the output of the steam generator 36 will be alow-grade steam of about 80 percent quality. However, the low-gradesteam may be of other percentages in quality. The low-grade steam isintroduced through the conduit 33, with the valve 38 open and the valve37 closed, to pass through the conduit 24 downwardly into the well 16.The low-grade steam flows into the area of the well 16 below the packer23.

The hot water phase separates from the steam phase in the lower portionof the well 16 below the packer 23. It is preferred for convenience toeffect the separation of the hot water phase from the steam phase withinthe well 16. This separation of phases, however, may be effected atother places than in the well 16.

The separated steam phase flows upwardly through the conduit 28 and openvalve 29 into the conduit 26. The valve in the conduit 26 is closed atthis time. As a result, the steam flows from the openings 27 in theconduit 26 and then through the openings 21 into the strata 4 11. Thisflow of steam heats the strata 11 and the connate fluids therein for afirst period. 7

The pressure of the steam in the conduit 24 causes the hot water in thewell 16 below the packer 23 to be forced through the openings 22 intothe strata 12. Thus, the hot water phase separated from the low-gradesteam forms a hot water drive in the strata 12 in the first period. Thishot water drive moves the oil in the strata 12 toward the well 17 fromwhich it is produced through the conduit 44.

After an amount of steam enters the strata 11 to stimulate oilproduction therefrom, the step of steam injection is terminated. At thistime, the valves 29 and 38 are closed, and valves 25 and 37 are opened.As a result, hot fluids which include oil are produced from the strata11 into the well 16 and then through the conduit 26 to a suitableproduction facility for a second period. Oil may be recovered from thesefluids. The hot fluids from the strata 11 are produced from the well 16until the rate of production has decreased to undesired amounts. Theinjection of the steam and subsequent production of hot fluids can againbe undertaken to repeat the first and second periods as often asdesired.

Simultaneously with the production of hot fluids from the strata 11 inthe second period, cold water from water supply 34 is passed through theconduits 32 and 24 into the well 16 below the packer 23. The conduit 24provides a separate flow path for the indirect heat exchange of thewater flowing downwardly in the conduit 24 into the strata 12 with thehot fluids produced into the well 16 from the strata 11.

The water flowing through the conduit 24 is heated to elevatedtemperatures by the hot fluids produced from the strata 11. For example,the well 17 may produce about 5 barrels of oil with 20 barrels of waterwhen it is cold. However, after being stimulated by the injection ofsteam, the well 16 may produce fluids at above 212 F. and at astimulated rate of barrels per day of oil withlOO barrels per day ofwater. Under these circumstances, the produced hot fluids could heatindirectly barrels of cold water per day from about 90 F. to about F.The amount of water which is heat exchanged with the produced hot fluidscan be about equal in volume to these hot fluids for good results.However, for acceptable results, the amount of the indirectly heatedwater can be such volume that all of the injected water is heated toabove the initial temperature of the subterranean reservoir 10. Thetemperature of the heated Water may be measured prior to injection, ifdesired, by any suitable means. The rate at which these amounts of Waterflow in the conduit 24 may be set by adjusting the valve 37. The waterflow may be varied in magnitude and with time. The rate of water flow inthe conduit 24 may be decreased as the temperature of the produced hotfluids decreases for the optimum transfer of heat between these fluids.

The hot fluids are indirectly cooled so that vapor-lock problems areavoided and no live steam is carried through the conduit 26 into surfaceproduction facilities. Thus, the dangers of handling live steam inproduction facilities are avoided.

The indirectly heated water from the conduit 24 flows through theopenings 22 into the strata 12 during the second period. As a result, acontinuous hot water drive is effected from the well 16 towards the well17 in the strata 12 during the first and second periods.

During the first and second periods, oil is produced from the strata 12through the openings 42 into the well 17. Thence, the produced oil isrecovered through the conduit 44 to the earths surface 18 for suitableutilization.

Thus, a cyclic steam injection and production of oil procedure effectedfrom the well 16 is combined with a continuous hot water drive for theproduction of oil from the well 17. The heat of the produced hot fluidsfrom the well 16 is employed in the second period to continue the hotwater drive in the strata 12 associated with steam injection during thefirst period. Thus, a functional combination is established, by thesteps of the present method, between the cyclic steam injection-oilproduction procedure carried out in the strata 11 and the continuing hotwater drive carried out in the strata 12.

It will be apparent that the strata 11 adjacent the well 17 may be steamstimulated in a manner similar to that described relative to the well16. Additionally, if desired, the present method may be continued to bepracticed until the formation adjacent the well 17 is heated by thecyclic steam injection from the well 16. After steam stimulating thewell 16 in the described manner, a continuous steam drive may beestablished in the strata 11 from the well 16 towards the well 17 withproduced oil recovered through conduit 46. Various other alterations ofthe present steps will be apparent to a person skilled in the art.

It will be apparent that the present method may be carried on in morethan two wells. A pattern of wells may be used wherein one or more wellsare employed in the manner of the well 16 and one or more wells areemployed in the manner of the well 17 in carrying out the priorlydescribed steps of the present method.

There has been provided herein a method which combines with greatfacility the cyclic steam injection-oil production procedure with acontinued hot water drive for producing oil from a subterraneanreservoir. This com- *bination is effected with avoidance of theproblems previously encountered by injecting low-grade steam in a cyclicinjection-oil production procedure. Additionally, the formally requiredexternally supplied heat for providing a continuous hot water drive isalso avoided.

From the foregoing, it will be apparent that a method is provided forthe production of oil from a subterranean reservoir which providescertain advantages over prior procedures. It will be understood thatcertain features and alterations of disclosed steps may be employedwithout departing from the spirit of the present invention. This iscontemplated by, and is within the scope of, the appended claims.Additionally, it is intended that the present description is to be takenas a means of illustration, and not as alimitation, of the presentmethod.

What is claimed is:

1. A method for producing oil from a subterranean reservoir having upperand lower oil-bearing permeable strata penetrated by spaced first andsecond wells which comprises the steps of:

(a) heating an aqueous liquid to a temperature sufficient to produce alowgrade steam containing a hot water phase at the pressure at whichthese fluids are to be injected into the strata;

(b) separating the hot water phase from the steam phase;

(c) injecting said steam phase into the upper strata, and injecting saidhot water phase into the lower strata, via the first well, for a firstperiod;

((1) producing hot fluids which include oil from the upper strata, viathe first well, for a second period, and simultaneously passing water ata temperature less than the temperature of said hot fluids through aseparate flow path in indirect heat exchange with the said hot fluids,in the second period;

(e) injecting said indirectly heated water into the lower strata, viathe first well, to effect a continuous hot water drive from the firstwell toward the second well in the lower strata, during the first andsecond periods; and

(f) producing oil from the lower strata via the second well.

2. The method of claim 1 wherein the amount of said water which ispassed in heat exchange with said hot fluids in step (d) is about equalin volume to said hot fluids.

3. The method of claim 1 wherein the amount of said water which ispassed in heat exchange with said hot fluids in step (d) is such thatall of the injected water has been heated to above the initialtemperature of the subterranean reservoir.

4. A method for producing oil from a subterranean reservoir having upperand lower oil-bearing permeable strata penetrated by spaced first andsecond wells which comprises the steps of:

(a) heating an aqueous liquid to a temperature sufficient to produce alow-grade steam containing a hot water phase at the pressure at whichthese fluids are to be injected into the strata;

(b) passing the low-grade steam into the first well and thereinseparating the hot water phase from the steam phase;

(0) injecting said steam phase into the upper strata, and injecting saidhot water phase into the lower strata, via the first well, for a firstperiod;

(d) producing hot fluids which include oil from the upper strata, viathe first well, for a second period, and simultaneously passing water ata temperature less than the temperature of said hot fluids thnough aseparate flow path within said first well in indirect heat exchange withsaid hot fluids, in the second period;

(e) injecting said indirectly heated water into the lower strata, viathe first well, to effect a continuous hot Water drive from the firstwell toward the second well in the lower strata, during the first andsecond periods; and

(f) producing oil from the lower strata via the second well.

5. The method of claim 4 wherein the amount of said water which ispassed in heat exchange with said hot fluids in step (d) is about equalin volume to said hot fluids.

6. The method of claim 4 wherein the amount of said water which ispassed in heat exchange with said hot fluids in step (d) is such thatall of the injected water has been heated to above the initialtemperature of the subterranean reservoir.

7. The method of chain 4 wherein said steam phase is continuouslyinjected into the upper strata to provide a continuous steam drive fromthe first well toward the second well in the upper strata after theupper strata of the subterranean reservoir is heated to elevatedtemperatures about the second well by the injected steam phase.

References Cited UNITED STATES PATENTS 1,491,138 4/1924 Hixon l66--112,734,579 2/1956 Elkins 166-11 3,167,120 l/1965 Pryor 166-11 3,193,0097/1965 Wallace et a1. 16611 3,259,186 7/1966 Dietz 166-11 3,294,16712/1966 Vogel 166-11 3,323,590 6/1967 Gilchrist et a1. 16611 STEPHEN J.NOVOSAD, Primary Examiner.

US. 01. X.R.

